Aromatic thioether acylation method

ABSTRACT

The present invention relates to a process for the acylation of an aromatic thioether. In its preferred variant, the invention resides in a process for the condensation of acetic anhydride or acetyl chloride with thioanisole. The process for the acylation of an aromatic thioether according to the invention is characterised in that it consists in reacting said thioether with an acylating agent chosen from the group formed by the halides of carboxylic acids and the anhydrides of carboxylic acids, in the presence of an effective quantity of an acid zeolite.

This application is an application under 35 U.S.C. Section 371 ofInternational Application Number PCT/FR96/01763, filed on Nov. 8, 1996.

In its preferred variant, the invention resides in a process for thecondensation of acetic anhydride or acetyl chloride with thioanisole.

In the following account of the present invention, the term "aromaticthioether" means an aromatic compound of which a hydrogen atom directlylinked to the aromatic nucleus is replaced by a thioether group, and theterm "aromatic compound" means the conventional notion of aromaticity asdefined in the literature, particularly by Jerry MARCH, Advanced OrganicChemistry, 4th edition, John Wiley and Sons, 1992, pp 40 et seq.

A process has been found, and this constitutes the subject matter of thepresent invention, for the acylation of an aromatic thioether,characterised in that it consists in reacting said thioether with anacylating agent chosen from the group formed by the halides ofcarboxylic acids and the anhydrides of carboxylic acids, in the presenceof an effective quantity of an acid zeolite.

More specifically, the present invention relates to a process for theacylation of an aromatic thioether having the general formula (I):##STR1## in which: A symbolises the radical of a ring forming all orpart of an aromatic, monocyclic or polycyclic carbocyclic system, asystem containing at least one SR' group: said cyclic radical may bearone or more substituents,

R represents one or more substituents which may be the same ofdifferent,

R' represents an optionally substituted hydrocarbon radical having 1 to24 carbon atoms, which may be a saturated or unsaturated, linear orbranched acyclic aliphatic radical, a saturated, unsaturated oraromatic, monocyclic or polycyclic cycloaliphatic radical, a saturatedor unsaturated, linear or branched aliphatic radical bearing a cyclicsubstituent,

R' and R may form a ring optionally containing another heteroatom,

n represents the number of substituents on the ring.

In the present disclosure, the term "thioether groups" designates, in asimplified manner, groups of the --S--R' type in which R' has themeaning given above. R' therefore represents both an acyclic orcycloaliphatic, saturated, unsaturated or aromatic aliphatic radical anda saturated or unsaturated aliphatic radical bearing a cyclicsubstituent.

The aromatic thioether used in the process of the invention correspondsto formula (I) in which R' represents a saturated or unsaturated, linearor branched acyclic aliphatic radical.

More preferably, R' represents a linear or branched alkyl radical having1 to 12 carbon atoms, preferably 1 to 6 carbon atoms: the hydrocarbonchain may optionally be interrupted by a heteroatom (for example,oxygen), by a functional group (for example --CO--) and/or may bear asubstituent (for example, a halogen).

The saturated or unsaturated, linear or branched acyclic aliphaticradical may optionally bear a cyclic substituent. The term ringpreferably means a saturated, unsaturated or aromatic carbocyclic ring,preferably cycloaliphatic or aromatic, particularly cycloaliphaticcontaining 6 carbon atoms in the ring or benzene ring.

The acyclic aliphatic radical may be linked to the ring by a valencybond, a heteroatom or a functional group, and examples are given below.

The ring may optionally be substituted and examples of cyclicsubstituents may include, inter alia, substituents such as R₁ themeaning of which is specified for formula (Ia).

R' may also represent a carbocyclic radical which is saturated orcontains 1 or 2 unsaturations in the ring, generally having 3 to 8carbon atoms, preferably 6 carbon atoms in the ring, said ring may besubstituted with substituents such as R.

R' may also represent an aromatic carbocyclic radical, preferablymonocyclic, generally having at least 4 carbon atoms, preferably 6carbon atoms in the ring; said ring may be substituted with substituentssuch as R.

The process of the invention applies more particularly to aromaticthioethers of formula (I) in which R' represents a linear or branchedalkyl radical having 1 to 4 carbon atoms or a phenyl radical.

Examples of radicals R' preferred according to the invention includemethyl and ethyl radicals.

In the general formula (I) of aromatic thioethers, the radical A mayrepresent the radical of an aromatic, monocyclic, carbocyclic compoundhaving at least 4 carbon atoms and preferably 6 carbon atoms, or theradical of a polycyclic carbocyclic compound which may be composed of atleast 2 aromatic carbocycles and forming, amongst themselves, ortho- orortho- and pericondensed systems, or of at least 2 carbocycles of whichat least one is aromatic and forming amongst themselves ortho- or ortho-and pericondensed systems. More particularly, a naphthalene radical maybe mentioned.

The radical A may bear one or more substituents on the aromatic nucleus.

The number of substituents present on the ring depends on the carboncondensation of the ring and on the presence or absence of unsaturationson the ring.

The maximum number of substituents capable of being borne by a ring iseasily determined by the man skilled in the art.

In the present disclosure, the term "more" generally means less than 4substituents on an aromatic nucleus. Examples of substituents are givenbelow but this list is in no way limiting. Any substituent may bepresent on the ring provided that it does not interfere with the desiredproduct.

The process of the invention applies more particularly to the aromaticthioethers corresponding to formula (Ia): ##STR2## in which: n is anumber lower than or equal to 4, preferably equal to 0, 1 or 2,

the radical R' represents a linear or branched alkyl radical having 1 to6 carbon atoms, preferably 1 to 4 carbon atoms, optionally interruptedby an oxygen atom or a carbonyl group and/or bearing one or more halogenatoms, preferably a chlorine atom, or a phenyl radical,

the radical(s) R represent one of the following atoms or groups:

a hydrogen atom,

a linear or branched alkyl radical having 1 to 6 carbon atoms,preferably 1 to 4 carbon atoms such as methyl, ethyl, propyl, isopropyl,butyl, isobutyl, sec.-butyl, tert.-butyl,

a linear or branched alkenyl radical having 2 to 6 carbon atoms,preferably 2 to 4 carbon atoms, such as vinyl, allyl,

a cyclohexyl or benzyl radical,

a linear or branched alkoxy radical having 1 to 6 carbon atoms,preferably 1 to 4 carbon atoms such as methoxy, ethoxy, propoxy,isopropoxy, butoxy, isobutoxy, sec.-butoxy, tert.-butoxy radicals,

an acyl group having 2 to 6 carbon atoms,

a hydroxyl group,

a halogen atom, preferably a fluorine, chlorine or bromine atom,

a trifluoromethyl radical,

an amine group,

two groups R placed on two vicinal carbon atoms may together, and withthe carbon atoms which bear them, form a benzene ring,

the radicals SR' and R and the two successive atoms of the benzene ringmay form, amongst themselves, a ring having 5 to 7 atoms, optionallycontaining another heteroatom.

If n is greater than or equal to 1, the radicals R' and R and the 2successive atoms of the benzene ring may be linked together by analkylene, alkenylene or alkenylidene radical having 2 to 4 carbon atomsto form a saturated, unsaturated or aromatic heterocycle having 5 to 7carbon atoms, One or more carbon atoms may be replaced by anotherheteroatom, preferably sulphur. Thus, the radicals SR' and R mayrepresent a methylenedithio or an ethylenedithio radical.

The process of the invention applies more particularly to the aromaticthioethers corresponding to formula (la) in which n is equal to 1, theradical R' represents an alkyl radical having 1 to 4 carbon atoms and Rrepresents a hydrogen atom, an alkyl or alkoxy radical having 1 to 4carbon atoms or a hydroxyl group.

By way of illustration of compounds corresponding to formula (I), thefollowing may be mentioned more particularly:

thioanisole,

o-thiocresol,

m-thiocresol,

p-thiocresol,

2-thioethyinaphthalene,

S-phenylthioacetate,

3-(methylmercapto)aniline,

S-phenylthiopropionate

The compound to which the process of the invention applies moreparticularly is thioanisole.

It is desirable to use an aromatic thioether having good chemicalpurity. A purity of at least 97% is desirable.

It may prove necessary to purify the starting substrate, for example, bydistillation, in so far as it contains impurities likely to poison thezeolite catalyst.

The acylating reagent is chosen from the group formed by the halides ofcarboxylic acids and the anhydrides of carboxylic acids.

The said derivatives are derived preferably from saturated orunsaturated, linear or branched aliphatic carboxylic acids or fromoptionally substituted, saturated or unsaturated cycloaliphatic acids.

More particularly, they correspond to the formula (II): ##STR3## inwhich: R₁ represents:

a saturated or unsaturated, linear or branched aliphatic radical having1 to 24 carbon atoms, a saturated or unsaturated, monocyclic orpolycyclic cycloaliphatic radical having 3 to 12 carbon atoms;

X' represents:

a halogen atom, preferably a chlorine or bromine atom,

a --O--CO--R₂ radical where R₂, which may be the same as or differentfrom R₁, has the same meaning as R₁ ; R₁ and R₂ together may form asaturated or unsaturated, linear or branched aliphatic divalent radicalhaving at least 2 carbon atoms.

The term cyclic substituent refers to the description given above.

More preferably, R₁ represents a linear or branched alkyl radical having1 to 12 carbon atoms, preferably 1 to 6 carbon atoms: the hydrocarbonchain may optionally be interrupted by a heteroatom (for example,oxygen), by a functional group (for example, --CO--), and/or may bear asubstituent (for example, a halogen or a CF₃ group).

R₁ represents preferably an alkyl radical having 1 to 4 carbon atoms,such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec.-butyl,tert.-butyl.

R₁ also represents an alkenyl radical having 2 to 10 carbon atoms, suchas vinyl, propenyl, butenyl, pentenyl, hexenyl, octenyl, decenyl.

The radical R₁ also represents a non-aromatic radical, preferablycycloaliphatic, for example, a cyclohexyl radical, which may optionallybe substituted. Any substituent may be present on the ring provided thatit does not interfere with the desired product.

More particular examples of substituents include, in particular:

a linear or branched alkyl radical having 1 to 6 carbon atoms,preferably 1 to 4 carbon atoms, such as methyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec.-butyl, tert.-butyl,

a linear or branched alkoxy radical having 1 to 6 carbon atoms,preferably 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy,isopropoxy, butoxy, isobutoxy, sec.-butoxy, tert.-butoxy radicals,

a halogen atom, preferably a fluorine, chlorine or bromine atom,

The preferred acylating agents are acid anhydrides. They correspond moreparticularly to the formula (II) in which R₁ and R₂ are the same andrepresent an alkyl radical having 1 to 4 carbon atoms, optionallybearing halogen atoms, preferably chlorine.

If the acylating agent is an acid halide, it corresponds preferably toformula (II) in which X' represents a chlorine atom and R₁ represents analkyl radical having 1 to 4 carbon atoms, preferably methyl or ethyloptionally bearing halogen atoms, preferably chlorine.

Examples of acylating agents corresponding to formula (II) include, moreparticularly:

acetic anhydride

propanoic anhydride

isobutyric anhydride

trifluoroacetic anhydride

trichloroacetic anhydride

monochloroacetyl anhydride

monochloroacetyl anhydride

acetyl chloride

monochloroacetyl chloride

dichloroacetyl chloride

propanoyl chloride

isobutanoyl chloride

pivaloyl chloride

crotonyl chloride.

In accordance with the process of the invention, the acylation reactionis carried out in the presence of a catalyst composed of an acidzeolite.

The term "zeolite" means a crystalline tectosilicate of natural orsynthetic origin, the crystals of which are the result of thethree-dimensional assembly of tetrahedral units of SiO₄ and TO₄ ; Trepresents a trivalent element such as aluminium, gallium, boron, iron,preferably aluminium

Zeolites of the aluminosilicate type are the most common.

Within the crystalline network, zeolites have a system of cavitieslinked together by channels with a well defined diameter which are knownas pores.

Zeolites may have a unidimensional, two-dimensional or three-dimensionalnetwork of channels.

In the process of the invention, a natural or synthetic zeolite may beused.

Examples of natural zeolites which may be used include, for example:chabazite, clinoptilolite, erionite, phillipsite, offretite.

Synthetic zeolites are particularly suitable for the use of theinvention.

Examples of synthetic zeolites with a unidimensional network include,amongst others, zeolite ZSM-4, zeolite L, zeolite ZSM-12, zeoliteZSM-22, zeolite ZSM-23, zeolite ZSM-48.

Examples of zeolites with a two-dimensional network used in preferenceinclude mordenite, ferrierite.

Zeolites with a three-dimensional network include more particularlyzeolite-β, zeolite Y, zeolite X, zeolite ZSM-5, zeolite ZSM-11,offretite.

Synthetic zeolites are used in preference, and more particularlyzeolites which take the following forms:

mazzite with an Si/Al molar ratio of 3.4,

zeolite L with an Si/Al molar ratio of 1.5 to 3.5,

mordenite with an Si/Al molar ratio of 5 to 150, preferably 10 to 100and even more preferably 10 to 25,

ferrierite with an Si/Al molar ratio of 3 to 10,

offretite with an Si/Al molar ratio of 4 to 8.5,

zeolites β with an Si/Al molar ratio greater than 8, preferably between10 and 3 5, and even more preferably between 12 and 35,

zeolites Y, particularly the zeolites obtained after a dealuminificationtreatment (for example, hydrotreatment, washing with hydrochloric acidor a treatment with SiCI₄) and more particularly zeolites US-Y with anSi/Al molar ratio greater than 3, preferably between 6 and 60,

zeolite X of the faujasite type with an Si/Al molar ratio of 0.7 to 1.5,

zeolites ZSM-5 or aluminium silicate with an Si/Al molar ratio of 10 to500,

zeolite ZSM-11 with an Si/Al molar ratio of 5 to 30.

Of all these zeolites, zeolites β are used in preference in the processof the invention.

The zeolites used in the process of the invention are known productsdescribed in the literature [cf. Atlas of zeolites structure types by W.M. Meier and D. H. Olson published by the Structure Commission of theInternational Zeolite Association (1992)].

It is possible to use commercially available zeolites or to synthesisethem according to processes described in the literature.

Reference may be made to the above-mentioned Atlas, and moreparticularly, for the preparation:

of zeolite L, to the publication by Barrer R. M. et al., Z.Kristallogr., 128, pp. 352 (1969)

of zeolite ZSM-12, to the US patent 3,832,449 and to the article byLaPierre et al., Zeolites 5, pp. 346 (1985),

of zeolite ZSM-22, to the publication by Kokotallo G. T. et at.,Zeolites 5, pp. 349 (1985),

of zeolite ZSM-23, to the U.S. Pat. No. 4,076,842 and to the article byRohrman A. C. et al., Zeolites 5, pp. 352 (1985),

of zeolite ZSM-48, to the works by Schlenker J. L. et al., Zeolites 5,pp. 355 (1985),

of zeolite β, to the U.S. Pat. No. 3,308,069 and to the article byCaullet P. et al., Zeolites 12, pp 240 (1992),

of mordenite, to the works by Itabashi et al., Zeolites 6, pp 30 (1986),

of zeolites X and Y, to the U.S. Pat. Nos. 2,882,244 and 3,130,007respectively,

of zeolite ZSM-5, to the U.S. Pat. No. 3,702,886 and to the article byShiralkar V. P. et al., Zeolites 9, pp. 363 (1989),

of zeolite ZSM-11, to the works by Harrison I. D. et al., Zeolites 7,pp. 21 (1987).

The zeolite constitutes the catalytic phase. It may be used alone or inmixture with a mineral matrix. In the description, the term "catalyst"will mean the catalyst made wholly of zeolite or in mixture with amatrix prepared according to methods known by the man skilled in theart.

To this end, the matrix may be chosen from metal oxides such asaluminium, silicon and/or zirconium oxides, or from clays and moreparticularly kaolin, talc or montmorillonite.

In the catalyst, the active phase content represents 5 to 100% of theweight of the catalyst.

The catalysts may take different forms in the process of the invention:powder, formed products such as granules (for example, extrudates orbeads), pellets which are obtained by extrusion, moulding, compacting orany other type of known process. In practice, on an industrial scale,granules or beads are the forms having most advantages both in terms ofefficiency and in terms of convenience of use.

Whatever the zeolite chosen, a treatment is carried out if necessarywhich renders it acid.

To this end, conventional treatments are used.

Thus, alkaline cations may be exchanged by submitting the zeolite to atreatment carried out with ammonia thus leading to an exchange of thealkaline cation by an ammonium ion, then calcining the exchanged zeolitein order to decompose the ammonium cation thermally and to replace it byan H⁺ ion.

The amount of ammonia to be used is at least equal to the amount neededto exchange all the alkaline cations for NH₄ ⁺ ions.

At least 10⁻⁵ to 5.10⁻³ mole of ammonia per gram of zeolite aretherefore used.

The exchange reaction of the cation which can be exchanged for NH₄ ⁺ iscarried out at a temperature between ambient temperature and the refluxtemperature of the reaction medium. The operation lasts a few hours andmay be repeated.

The zeolite may also be acidified by undergoing a conventional acidtreatment. This treatment may be carried out by adding an acid such as,in particular, hydrochloric acid, sulphuric acid, nitric acid,perchloric acid, phosphoric acid and trifluoromethane sulphonic acid.

According to a preferred method of operating, the zeolite is acidifiedby passage of a volume of acid having a normality between 0.1 and 2 Nper gram of zeolite of between 10 ml/g and 100 ml/g. This passage may becarried out in a single stage or preferably in several successivestages.

In accordance with the invention, the acylation reaction is carried outadvantageously in the liquid phase containing the aromatic thioether andthe acylating agent, in the presence of the catalyst.

One of the starting reagents may act as the reaction solvent but it isalso possible to use an organic solvent.

Examples of solvents suitable for the present invention include, inparticular, aliphatic or aromatic, halogenated or non-halogenatedaliphatic hydrocarbons, aliphatic, cycloaliphatic or aromatic etheroxides.

Examples of aliphatic hydrocarbons include, more particularly, theparaffins such as, in particular, hexane, heptane, octane, nonane,decane, undecane, dodecane, tetradecane or cyclohexane, and naphthaleneand aromatic hydrocarbons and more particularly aromatic hydrocarbonssuch as, in particular, benzene, toluene, xylenes, cumene, petroleumfractions composed of a mixture of alkylbenzenes, particularly fractionsof the Solvesso® type.

The aliphatic or aromatic halogenated hydrocarbons include, moreparticularly, perchlorinated hydrocarbons such as, in particular,tetrachloroethylene, hexachloroethane, partially chlorinatedhydrocarbons such as dichioromethane, chloroform, 1,2-dichloroethane,1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane,trichloroethylene, 1-chlorobutane, 1,2-dichlorobutane;monochlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene,1,4-dichlorobenzene, 1,2,4-trichlorobenzene or mixture of differentchlorobenzenes; bromoform, bromoethane or 1,2-dibromoethane;monobromobenzene or mixtures of monobromobenzene with one or moredibromobenzenes: 1-bromonaphthalene.

Organic solvents that may also be used include aliphatic, cycloaliphaticor aromatic ether oxides and, more particularly, diethyl oxide, dipropyloxide, dilsopropyl oxide, dibutyl oxide, methyltertiobutylether,dipentyl oxide, diisopentyl oxide, the dimethylether of ethylene glycol(or 1,2-dimethoxyethane), the dimethyl ether of diethylene glycol (or1,5-dimethoxy 3-oxapentane); benzyl oxide; dioxane, tetrahydrofuran(THF).

Examples of aprotic, more polar organic solvents that may also be usedin the process of the invention include, more particularly, nitratedcompounds such as, for example, nitromethane, nitroethane,1-nitropropane, 2-nitropropane or mixtures thereof, nitrobenzene;aliphatic or aromatic nitriles such as acetonitrile, propionitrile,butane nitrile, isobutane nitrile, benzonitrile, benzyl cyanide, linearor cyclic carboxamides such as N,N-dimethylacetamide (DNAC),N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide or1-methyl-2-pyrrolidinone (NMP); dimethylsulphoxide (DMSO),tetramethylene sulphone (sulpholane); hexamethylphosphotriamide (HMPT).

The preferred solvents are: dichloromethane, tetrachloromethane, THF anddiethyl oxide.

It is also possible to use a mixture of organic solvents.

In preference, the starting substrate is used as the reaction solvent.

As mentioned above, the aromatic thioether is allowed to react with anacylating agent, optionally in the presence of a reaction solvent asdefined and in the presence of a zeolite catalyst.

The ratio between the number of moles of aromatic thioether and thenumber of moles of acylating agent may vary because the substrate mayact as reaction solvent. Thus, the ratio may be from 0.1 to 10, and ispreferably between 0.5 and 4.0.

The amount of catalyst that is used in the process of the invention mayvary widely.

If the process is carried out batchwise, the catalyst may represent 0.01to 50%, preferably 5 to 25% by weight with respect to the aromaticthioether used. However, if the process is carried out continuously, forexample by allowing a mixture of aromatic thioether and acylating agentto react on a fixed bed of catalyst, these ratios of catalyst/aromaticthioether have no meaning and at a given moment it is possible to have aweight excess of catalyst with respect to the starting aromaticthioether.

The amount of organic solvent used is generally chosen such that theratio between the number of moles of organic solvent and the number ofmoles of aromatic thioether is preferably between 0 and 100, and evenmore preferably between 0 and 50.

The temperature at which the acylation reaction is brought into effectdepends on the reactivity of the starting substrate and that of theacylating agent.

It is between 20° C. and 300° C., preferably between 40° C. and 200° C.

Generally speaking, the reaction is carried out at atmospheric pressure,but lower or higher pressures may also be suitable. Operations arecarried out under autogenous pressure if the reaction temperature ishigher than the boiling point of the reagents and/or the products.

From a practical point of view, the process may be used batchwise orcontinuously.

According to the first variant, there are no constraints regarding theuse of the reagents. They may be introduced in any order.

After the reagents have been brought into contact, the reaction mixtureis brought to the desired temperature.

The other variant of the invention consists in carrying out the reactioncontinuously in a tubular reactor containing the solid catalyst arrangedon a fixed bed.

The aromatic thioether and the acylating agent may be introducedseparately or in mixture into the reactor.

They may also be introduced in a solvent of the kind mentioned above.

The residence time of the material flow on the catalyst bed is between15 mn and 10 hours, for example, and preferably between 30 mn and 5hours.

At the end of the reaction, a liquid phase is recovered containing theacylated aromatic thioether which may be recovered in a conventionalmanner, by distillation or recrystallisation in an appropriate solvent,for example water or alcohols (methanol, ethanol) after excess reagentshave been removed beforehand.

The process of the invention is particularly suitable for thepreparation of 4-(methylthio)acetophenone, by acetylation ofthioanisole.

An advantage of the process of the invention is that the acylationreaction is carried out without S-dealkylation of the starting aromaticthioether.

The examples that follow illustrate the invention yet without limitingits scope.

In the examples, the yields mentioned correspond to the followingdefinition: ##EQU1##

The examples that follow illustrate the invention yet without limitingits scope.

EXAMPLE 1

In this example, the zeolite used is zeolite β with an Si/Al molar ratioof 12.5 sold by PQ Zeolites under the reference CVB 811BL25.

The following are charged to a closed 30 ml reactor:

5 g (40 mmol) of thioanisole sold by Aldrich (purity=97%),

2.05 g (20 mmol) of acetic anhydride,

0.5 g of said zeolite β, calcined beforehand at 550° C. under a currentof dry air.

The reactor is heated to 90° C. for 8 hours.

After 8 hours, the reaction mixture is filtered, then analysed by gaschromatography.

A reaction yield of 60% is obtained.

EXAMPLE 2

The following are charged to a closed 30 ml reactor:

35 g (282 mmol) of said thioanisole,

28.7 g (282 mmol) of acetic anhydride,

3.5 g of the zeolite β described in Example 1, calcined beforehand at550° C. under a current of dry air.

The reactor is heated to 90° C. for 8 hours.

After 12 hours, the reaction mixture is filtered, then analysed by gaschromatography.

A reaction yield of 45% is obtained.

EXAMPLE 3

The following example is a comparative example.

The following are charged to a closed 30 ml reactor:

2.5 g of acetic acid,

1 ml of thioanisole in 50 ml of chlorobenzene.

0.5 g of the zeolite β described in Example 1 are then added.

After 10 hours at 200° C., no formation of acetothioanisole is detected.

What is claimed is:
 1. A process for the acylation of an aromaticthioether, comprising the step of reacting said thioether with anacylating agent selected from the group consisting of the halides ofaliphatic carboxylic acids and the anhydrides of aliphatic carboxylicacids, in the presence of an effective quantity of an acid zeolite, saidaromatic thioether having the general formula (I): ##STR4## wherein: Asymbolizes the radical of a ring forming all or part of an aromatic,monocyclic or polycyclic carbocyclic system, a system containing atleast one SR' group;the R groups which are the same or different,represent:a hydrogen atom a linear or branched alkyl radical having 1 to6 carbon atoms, a linear or branched alkenyl radical having 2 to 6carbon atoms, a cyclohexyl or benzyl radical, a linear or branchedalkoxy radical having 1 to 6 carbon atoms, an acyl group having 2 to 6carbon atoms, a hydroxyl group, a halogen atom, a trifluoromethylradical, or an amine group: R' represents an optionally substitutedhydrocarbon radical having 1 to 24 carbon atoms, and n is 0 or a numberlower than or equal to
 4. 2. A process according to claim 1, wherein R'is a saturated or unsaturated, linear or branched, acyclic aliphaticradical; a saturated, unsaturated or aromatic, monocyclic or polycyclic,cycloaliphatic radical; or a saturated or unsaturated, linear orbranched aliphatic radical.
 3. A process according to claim 2, whereinR' represents:a linear or branched alkyl radical having 1 to 12 carbonatoms, a saturated or unsaturated, linear or branched, acyclic aliphaticradical bearing a substituted cyclic substituent; a carbocyclic radicalwhich is saturated or contains 1 or 2 unsaturations in the ring, having3 to 8 carbon atoms in the ring; said ring being optionally substituted,or an aromatic carbocyclic radical, having at least carbon atoms in thering; said ring being optionally substituted.
 4. A process according toclaim 3, wherein R' represents:a saturated or unsaturated, linear orbranched, acyclic aliphatic radical, having 1 to 6 carbon atoms; acarbocyclic radical which is saturated or contains 1 or 2 unsaturationsin the ring, having 6 carbon atoms in the ring; or a phenyl group.
 5. Aprocess according to claim 4, wherein R' represents a linear or branchedalkyl radical having 1 to 4 carbon atoms.
 6. A process according toclaim 5, wherein R' is methyl or phenyl.
 7. A process according to claim1, wherein A represents the radical of a monocyclic, aromaticcarbocyclic compound having at least 6 carbon atoms or the radical of apolycyclic carbocyclic compound; the radical A optionally bearing one ormore substituents on the aromatic nucleus.
 8. A process according toclaim 1, wherein A represents the radical of a monocyclic, aromaticcarbocyclic compound having 6 carbon atoms.
 9. A process according toclaim 1, wherein the radicals SR' and R and the two successive atoms ofthe benzene ring form, amongst themselves, a ring having 5 to 7 atoms.10. A process according to claim 1, wherein:n is a number equal to 0, 1,or 2, the radical R' represents a linear or branched alkyl radicalhaving 1 to 4 carbon atoms, optionally interrupted by an oxygen atom ora carbonyl group or bearing one or more chlorine atom, or a phenylradical, the radical(s) R represent:methyl, ethyl, propyl, isopropyl,butyl, isobutyl, sec.-butyl, tert.-butyl, vinyl, allyl, methoxy, ethoxy,propoxy, isopropoxy, butoxy, isobutoxy, sec.-butoxy, tert.-butoxy, afluorine, chlorine, or bromine atom.
 11. A process according to claim 1,wherein n is equal to 1, the radical R' represents an alkyl radicalhaving 1 to 4 carbon atoms and R represents a hydrogen atom, an alkyl oralkoxy radical having 1 to 4 carbon atoms or a hydroxyl group.
 12. Aprocess according to claim 11, wherein the aromatic thioether isthioanisole.
 13. A process according to claim 1, wherein the acylatingagent corresponds to the formula (II): ##STR5## wherein: R₁ represents:asaturated or unsaturated, linear or branched aliphatic radical having 1to 24 carbon atoms; and X' represents:a halogen atom or a radical--O--CO--R₂ where R₂, which is the same as or different from R₁, has thesame meaning as R₁.
 14. A process according to claim 13, wherein theacylating agent corresponds to the formula (II) in which the X'represents a chlorine atom and R₁ represents a linear or branched alkylradical having 1 to 12 carbon atoms; the hydrocarbon chain beingoptionally interrupted by a heteroatom or by a functional group orbearing substituents; X' represents an --O--CO--R₂ radical in which R₁and R₂ are the same and represent an alkyl radical having 1 to 4 carbonatoms optionally bearing halogen atoms.
 15. A process according to claim13, wherein the acylating agent is:acetic anhydride, propanoicanhydride, isobutyric anhydride, trifluoroacetic anhydride,trichloroacetic anhydride, monochloroacetyl anhydride, dichloroacetylanhydride, acetyl chloride, monochloroacetyl chloride, dichloroacetylchloride, propanoyl chloride, isobutanoyl chloride, pivaloyl chloride,or crotonyl chloride.
 16. A process according to claim 1, wherein thezeolite is chabazite, clinoptilolite, erionite, mordenite, phillipsite,or offretite.
 17. A process according to claim 1, wherein the zeolite isa synthetic zeolite with a unidimensional network.
 18. A processaccording to claim 17, wherein the zeolite is zeolite ZSM-4, zeolite L,zeolite ZSM-12, zeolite ZSM-22, zeolite ZSM-23, or zeolite ZSM-48.
 19. Aprocess according to claim 1, wherein the zeolite is a synthetic zeolitewith a two-dimensional network.
 20. A process according to claim 19,wherein the zeolite is mordenite, or ferrierite.
 21. A process accordingto claim 1, wherein the zeolite is a synthetic zeolite with athree-dimensional network.
 22. A process according to claim 21, whereinthe zeolite is zeolite-β, zeolite Y, zeolite X, zeolite ZSM-5, zeoliteZSM-11, or offretite.
 23. A process according to claim 1, wherein thezeolite is a zeolite β with an Si/Al molar ratio greater than 8, or azeolite US-Y with an Si/Al molar ratio greater than
 3. 24. A processaccording to claim 23, wherein the Si/Al molar ratio of the zeolite β isbetween 12 and 35, and the Si/Al molar ratio of the, zeolite US-Y isbetween 6 and
 60. 25. A process according to claim 1, wherein theacylation is carried out in an aqueous medium or in the presence of anoptionally halogenated organic solvent.
 26. A process according to claim25, wherein the solvent is an aliphatic or aromatic hydrocarbon, analiphatic, cycloaliphatic or aromatic ether oxide, an aprotic polarsolvent, a nitrated compound, an aliphatic or aromatic nitrile, a linearor cyclic carboxamide, dimethylsulphoxide, tetramethylenesulphone, orhexamethylphosphotriamide.
 27. A process according to claim 1, whereinthe ratio between the number of moles of aromatic thioether and thenumber of moles of acylating agent is between 0.1 and
 10. 28. A processaccording to claim 1, wherein the amount of zeolite represents 0.01 to50% by weight with respect to the aromatic thioether used.
 29. A processaccording to claim 1, wherein the acylation is carried out at atemperature of between 20° C. and 300° C.
 30. A process according toclaim 1, wherein the acylation is carried out batchwise or continuously.31. A process according to claim 13, wherein X' is chlorine or bromine.